1. Field of the Invention
The present invention relates to tanks thermally insulated with polymer foam, particularly water heaters. More particularly, the present invention relates to improved foam dams for use in constructing such insulated tanks.
Insulated tanks, particularly water heaters, as contemplated herein typically comprise a cylindrical water storage tank, a cylindrical shell coaxial with and radially spaced apart from the tank to form an annular space there between, and polymer foam insulating material in at least a portion of the annular space to provide thermal insulation for the tank. Polymer foam expanded directly in the annular space in particularly effective insulating material. A variety of polymer foams, such as epoxy foams and polyolefin foams, have been suggested and used as insulating material for water heaters. However, polyurethane foam is particularly preferred and widely used for the purpose. Employing methods well understood, and widely applied, by those skilled in the art of manufacturing water heaters, polymer reactant compositions are readily reacted in place within a portion of the annular space between the tank and shell to form polyurethane foam which expands to fill the space available to it. Briefly, a polyol resin-foaming agent mixture is brought into intimate contact with an isocyanate compound to form a liquid reaction mixture in the annular space between the tank and the shell. The isocyanate and polyol react in the presence of a catalyst, such as atmospheric moisture, to form polyurethane polymer in an exothermic reaction. The heat of reaction causes the foaming agent (a low boiling liquid such as FREON II) to vaporize. The vaporizing foaming agent causes the polymerizing liquid reaction mixture to froth and, as the polymerization reaction progresses, the froth becomes an expanding polymer foam. The polymer foam is initially fluid and quite sticky, and expands to fill substantially all the space between the tank and shell which is available to it. As the polymerization reaction continues to completion, the polyurethane polymer becomes stiff and the foam stabilizes into a rigid, closed-cell foam which fills the annular space surrounding the tank, and forms thermal insulation therefore. The amount of liquid polymer reactant composition injected into an annular space is selected, according to methods known to those skilled in the art, to ensure that the annular space is filled with polymer foam without creating an over pressure in the space.
Tanks, especially water heater tanks, have various appurtenances such as inlet, outlet, and drain fittings. Additionally, water heater tanks are provided with water heating and temperature control means. For example, a typical gas fired water heater is provided under the bottom with a heating chamber. A gas burner is placed in the heating chamber and water in the tank is heated with flame from the burner. Thus the burner has an open flame, and the heating chamber is hot. Sensors for thermostatic burner controls are placed within the interior of the tank through an opening in the tank wall provided therefore.
Polymer foams generally are flammable and if used as insulation for a water heater tank must be kept away from the heating element, such as the heating chamber and burner of a gas fired water heater. Polyurethane, in addition to being flammable, may emit toxic fumes upon combustion. Consequently, to avoid combustion hazards, polymer foam insulation material must be kept well away from hot surfaces, such as the heating chamber and burner associated with the water heater tank.
Over the years methods and devices have been developed in constructing water heaters for sealing an upper portion of an annular space, where expanding foam is to be placed, from a lower portion of the annular space near where the heating chamber and burner are located. Commonly, a foam dam device is placed in the annular space between the tank and shell at a selected position along the height of the cylindrical tank wall. The foam dam is in compressive sealing engagement with both the cylindrical inner wall of the shell and the cylindrical outer wall of the tank. Thus, the foam dam, and the upper portions of the shell wall and tank wall define an annular chamber. A liquid polymer reaction mixture is injected into the annular chamber and allowed to foam in place, to generate a thermally insulating jacket of polymer foam around the tank. The foam dam, in compressive sealing engagement with the walls of the tank and the shell, prevents the fluid foaming material from entering the lower portion of the annular space and from coming into contact with the heating chamber or burner.
A variety of foam dam devices have been proposed for such use in water heaters. These foam dams are generally either ring-shaped or have an elongated, flexible structure which can be wrapped into a ring shape.
U.S. Pat. No. 4,372,028, Clark et al, Feb. 8, 1983 discloses an elongated, flexible, expandable bag secured around the bottom edge of a tank. The bag is filled with a polymer reaction mixture and the shell is placed around the tank. The reaction mixture forms and expands to fill the bag which forms a collar which seals the space between the tank and a shell.
U.S. Pat. No. 4,447,377, to Denton, May 8, 1984, discloses a cylindrical envelope having a closed bottom and open top placed in the annular space between a cylindrical tank and a cylindrical shell, a polymer reaction mixture is placed in the envelope and is allowed to expand into a foam jacket surrounding the tank. The closed bottom of the envelope prevents the foam from contacting the heating chamber at the bottom of the tank.
U.S. Pat. No. 4,477,399, Tilton, Oct. 16, 1984, discloses an inflatable tube placed around the wall of a cylindrical tank. The tube is maintained at a desired elevation around the tank by either resting upon a stop member or by a stretch fit with the outer wall of the tank. A cylindrical shell is placed around the tank and tube, and the tube is inflated to form a seal between the shell and tank walls. The space above the tube is filled with expanding polymer foam. After use, the tube is deflated and, as desired, may be removed or left in place.
U.S. Pat. No. 4,979,637, Dec. 25, 1990 and U.S. Pat. No. 5,024,210, Jun. 18, 1991 and their divisional and parent applications, all to Nelson, disclose a sleeve of insulation material, such as fiberglass mat, around the lower portion of a cylindrical tank. The upper end of the sleeve is folded back upon itself to form a cuff. A cylindrical shell is placed concentrically around the tank such that the cuff is compressed between the shell and the tank, thus forming a seal in the annular space. A liquid polymer reaction mixture is injected into the annular space above the seal and is allowed to foam in place around the tank. The lower portion of the fiberglass sleeve insulates the lower portion of the tank.
U.S. Pat. No. 4,875,272, Oct. 24, 1989, U.S. Pat. No. 4,956,909, Sep. 18, 1990 and their divisions, all to Nelson, disclose an insulating and sealing device of insulation material, such as fiberglass or foamed material partially enclosed in an open-topped envelope of plastic or foil. The device is wedged-shaped in cross section, and the widest part of the wedge has a radial thickness greater than the width of the annular space, The device radially compressed between the wall of the tank and the wall of the shell. The sealing device is either an elongated member which is wrapped around the tank and held in place, as with an adhesive, or is a toroidial shaped member which is pushed into the annular space between the tank and the shell and held in place by compression against the walls of the tank and the shell.
U.S. Pat. No. 4,878,482, Pfeffer, Nov. 7, 1989, discloses a prefabricated bottom wall, such as styrofoam, in the annular space between a tank and shell. The styrofoam held in place at a selected elevation along the tank wall with an adhesive. The bottom wall has an outer sealing portion that is either integral with the body, or is a separate element affixed to the body. The outer sealing portion has sufficient compression or deflection to produce a seal in response to positioning the shell about the tank. The outer sealing portion may be material such as fiberglass or resilient polymer foam.
U.S. Pat. No. 4,890,762, Pfiffer, Jan. 2, 1990, discloses a flange extending from the lower portion of a tank into the annular space between the tank and a shell. A foam dam of flexible resilient material, such as fiberglass mat, is fixed around the tank and, in association with the flange, forms a seal in the annular space at the elevation of the flange.
U.S. Pat. No. 4,972,967, Nelson, Nov. 27, 1990, discloses a water heater construction including an inner tank surrounded in spaced apart relationship by an outer shell. An outer collar of insulation material is located in the annular space between the inner tank and shell at a preselected location along the height of the tank. The collar has a radial thickness greater than the radial width of the annular space and is compressed between the interior wall of the shell and the outer wall of the tank. The collar is either fixed in place prior to assembly of the tank and shell, or is pushed into the annular space between the tank and shell. Conveniently, stop means are used to maintain the collar at its preselected position in the annular space. The annular collar may be of compressible materials such as open cell polyurethane; closed cell foam; fiberglass; polyethylene envelopes of compressible materials; and other compressible materials.
U.S. Pat. No. 5,040,697, Aug. 20, 1991, to Nelson, discloses a water heater construction including an inner tank surrounded in spaced apart relationship by an outer shell. An outer collar of insulating material is located in the annular space between the tank and the shell. The collar has a radial thickness greater than the radial width of the annular space, and in one embodiment comprises a hollow tube of compressible material, such as polyurethane foam, formed into a ring-shaped collar, The collar is positioned in the annular space by being pushed down to its preselected location. A stop may be used in the annular space to locate the collar being pushed in, and the collar may be lubricated to ease the force necessary to push it.
While these collar and sleeve devices have been proposed, and some have been used commercially, as foam dams in construction of insulated tanks such as water heaters, a need continues to exist for an inexpensive foam dam device which is easy to use and may be accurately placed within an annular space between the tank and shell of a water heater or other insulated tank construction.